We've now written two papers (here and here) that indicate that the morphology–density relation is merely a product of the morphology–color relation and the color–density relation, but which contains little over and above that product. These papers were limited by our blunt
morphological tools; ie, we have quantitative measures of galaxy properties that are closely related to classical morphological classification, but not identical with it.
I realized that I can demonstrate the point directly with images of galaxies, as we did for our contribution to AAS 205, and let our readers do the morphological classification any way they like. I started to write this up.